<!DOCTYPE html>
<html>
<head>
<style>
.grid-container {
  width: 500px;
  /* 使用网格- */
  display: grid;
  /* 有3列,每列宽度自动平分 */
  grid-template-columns: auto auto auto;
  background-color: #2196F3;
  padding: 10px;
}
.grid-item {
  background-color: rgba(255, 255, 255, 0.8);
  border: 1px solid rgba(0, 0, 0, 0.8);
  font-size: 30px;
  text-align: center;
}
</style>
</head>
<body>

<div class="grid-container">
  <div class="grid-item">1</div>
  <div class="grid-item">2</div>
  <div class="grid-item">3</div>  
  <div class="grid-item">4</div>
  <div class="grid-item">5</div>
  <div class="grid-item">6</div>  
  <div class="grid-item">7</div>
  <div class="grid-item">8</div>
  <div class="grid-item">9</div>  
</div>

</body>
</html>
